A microelectromechanical system (MEMS) is a microdevice that integrates mechanical and electrical elements on a common substrate using microfabrication technology. The electrical elements are formed using known integrated circuit fabrication techniques, while the mechanical elements are fabricated using lithographic techniques that selectively micromachine portions of a substrate. Additional layers are often added to the substrate and then micromachined until the MEMS device is in a desired configuration. MEMS devices include actuators, sensors, switches, accelerometers, and modulators.
MEMS switches have intrinsic advantages over conventional solid-state counterparts such as field-effect transistor switches. The advantages include low insertion loss and excellent isolation. However, MEMS switches are generally much slower than solid-state switches. This speed limitation precludes applying MEMS switches in certain technologies, such as wireless communications, where sub-microsecond switching is required.
One type of MEMS switch includes a suspended connecting member, or beam, that is electrostatically deflected by energizing an actuation electrode. The deflected beam engages one or more electrical contacts to establish an electrical connection between isolated contacts. A beam anchored at one end while suspended over a contact at the other end is called a cantilevered beam. A beam anchored at opposite ends and suspended over one or more electrical contacts is called a bridge beam.
FIGS. 1-3 illustrate a prior art MEMS switch 10 that includes a bridge beam 12. Beam 12 is made up of structural portions 14 and a flexing portion 16. MEMS switch 10 further includes a pair of actuation electrodes 18A, 18B and a pair of signal contacts 20A, 20B that are each mounted onto a base 22.
Beam 12 is mounted to base 22 such that flexing portion 16 of beam 12 is suspended over actuation electrodes 18A, 18B and signal contacts 20A, 20B. Signal contacts 20A, 20B are not in electrical contact until a voltage is applied to the actuation electrodes 18A, 18B. As shown in FIG. 2, applying a voltage to actuation electrodes 18A, 18B causes the flexing portion 16 of beam 12 to move down until protuberances 21 on the flexing portion 16 engage signal contacts 20A, 20B to electrically connect signal contacts 20A, 20B. In other types of MEMS switches, signal contacts 20A, 20B are always electrically connected such that beam 12 acts as a shunt when beam 12 engages signal contacts 20A, 20B.
One drawback associated with MEMS switch 10 is that there is significant resistance between protuberances 21 on beam 12 and the pads that form signal contacts 20A, 20B. The considerable resistance between protuberances 21 and signal contacts 20A, 20B causes excessive insertion losses within MEM switch 10.
FIGS. 4 and 5 illustrate another prior art MEMS switch 30 that includes a bridge beam 32. MEMS switch 30 is similar to MEMS switch 10 in FIG. 1 in that MEMS switch 30 also includes a beam 32 that is made up of structural portions 34 and a flexing portion 36. MEMS switch 30 similarly includes a pair of actuation electrodes 38A, 38B and a pair of signal contacts 40A, 40B that are each mounted onto a base 42. Flexing portion 36 of beam 32 is suspended over actuation electrodes 38A, 38B and signal contacts 40A, 40B such that when a voltage is applied to actuation electrodes 38A, 38B, multiple protuberances 41 on flexing portion 36 move downward to engage signal contacts 40A, 40B.
MEMS switch 30 attempts to address the resistance problems associated with MEMS switch 10 by using more protuberances 41 on beam 32. The drawback with adding additional protuberances is that only a few of the protuberances 41 actually establish good electrical contact with signal contacts 20A, 20B. The remaining protuberances are in poor electrical contact with signal contacts 20A, 20B or do not even engage signal contacts 20A, 20B. Therefore, MEMS switch 30 still has considerable insertion loss.
FIGS. 6 and 7 illustrate a more recent prior art MEMS switch 50 that includes a bridge beam 52. MEMS switch 50 is similar to MEMS switches 10, 30 in FIGS. 1-4 in that MEMS switch 50 also includes a beam 52 that is made up of structural portions 54 and a flexing portion 56. MEMS switch 50 includes an actuation electrode 58 that is positioned below a surface 61 of base 66. Actuation electrode 58 extends below a pair of signal contacts 60A, 60B that are each mounted onto base 66. Signal contacts 60A, 60B include projections 62 that extend from respective bodies 63. The flexing portion 56 of beam 52 is suspended over projections 62 such that when actuation electrode 58 applies a voltage, multiple protuberances 65 on flexing portion 56 move downward to engage projections 62.
Placing actuation electrode 58 under projections 62 surrounds each protuberance 65 with pulling force when a voltage is applied to actuation electrodes 58. The space between projections 62 on each signal contact 60A, 60B further enhances the surrounding effect of the force generated by actuation electrode 58.
During operation of MEMS switch 50, the pulling force surrounding each protuberance 65 facilitates contact between each protuberance 65 and signal contacts 60A, 60B. The improved contact between protuberances 65 and signal contacts 60A, 60B minimizes insertion loss within MEMS switch 50.
One drawback associated with MEMS switch 50 is a greater distance between actuation electrode 58 and beam 52 as compared to other MEMS switches. The increased distance between actuation electrode 58 and beam 52 requires a much larger actuation voltage to be applied to actuation electrode 58 in order to manipulate beam 52. Increased actuation voltage is undesirable because more equipment and/or power are required to operate MEMS switch 50. The necessary additional equipment and power are especially problematic when MEMS switches are used in portable electronic devices powered by batteries.